The field is lightweight panels, connectors and tools used to construct mats that enable or enhance mobility across unstable terrain.
It is desirable to move heavy vehicles over unstable terrain during various events. These events may include environmental remediation, military maneuvers, or scientific exploration of environmentally fragile areas. Mat panels have been used successfully for applications that are similar to this, such as expedient aircraft runway repair. Mat panels of a preferred embodiment of this invention use fiberglass-reinforced plastic (FRP) material similar to that of a mat developed by the U.S. military for airfield pavement repair. Three U.S. patents resulted from development work on these military panels.
U.S. Pat. No. 4,404,244, System for Rapid Repair of Damaged Airfield Runways, to Springston, Sep. 13, 1983, describes a membrane of FRP prefabricated from several chopped fiberglass matting layers chemically bonded to woven fiberglass roving and impregnated with a polyester resin to yield a panel of a typical thickness of xe2x85x9c in. The anchoring system comprised special bushings fitted to holes along the edges of the panels for use with torque set rock bolts anchored to the edges of undamaged runway.
U.S. Pat. No. 4,605,337, Expedient Runway Surfacing with Post Tensioning System for Expeditionary Airfields, to Springston et al., Aug. 12, 1986, describes a system for building a runway with FRP panels that also uses a self-contained hydraulic tensioning system and a deadman earth anchor at each end of the runway to allow for expansion and contraction due to temperature and dynamic loads thereon.
U.S. Pat. No. 4,629,358, Prefabricated Panels for Rapid Runway Repair and Expedient Airfield Surfacing, to Springston et al., Dec. 16, 1986, provided an panel improved over that of the ""244 patent in that it was lighter in weight through the introduction of hollow inorganic silica spheres, commercially referred to as xe2x80x9cmicroballoons,xe2x80x9d in the plastic resin.
Much before the military panels were invented, the use of plastic for landing mats was patented. U.S. Pat. No. 2,653,525, Landing Mat, to McGuire, Sep. 29, 1953, provided an unusually configured mat made of xe2x80x9cfibrous reinforced plasticxe2x80x9d for use as a runway surface at an airfield.
U.S. Pat. No. 4,746,243, Apparatus and Method for Rapid Repair of Damaged Airfield Runways, to Perry, May 24, 1988, uses the concept of the military runway repair patents with a clamping system and a tapered edge to integrate the mat with existing undamaged runway.
Alternative materials for supporting heavy equipment include a board mat system detailed in U.S. Pat. No. 4,600,337, Board Mat System, to Sarver, Jul. 15, 1986, that uses wooden boards connected in a flexible strip to support heavy loads.
More recent inventions for supporting heavy construction equipment include mats of heavy tubular support designed to be emplaced by the vehicle they support as described in U.S. Pat. No. 6,007,271, Ground Pressure Distribution Mat, to Cole et al., Dec. 28, 1999.
Recent patents for mats that used FRP materials include two with novel means for interlocking the mat panels. U.S. Pat. No. 5,776,582, Load-Bearing Structures with Interlocking Edges, to Needham, Jul. 7, 1998, describes a series of pyramid-shaped elements along opposite edges of a panel designed to interlace with similar elements on an adjoining panel. U.S. Pat. No. 5,888,612, Load-Bearing Structures, to Needham et al., Mar. 30, 1999, describes a honeycombed rectangular panel having an L-shaped stepped down lip running nearly the full distance along a narrow end and only halfway along an adjacent longer side with a straight stepped down lip extending halfway along the side opposite the adjacent longer side but at the other end of that side.
For repair, one type of military mats are emplaced over craters filled with crushed-stone to effect rapid runway repairs. In these applications, the compacted crushed-stone layer carries the load of the aircraft and the FRP mat-serves as a debris cover and wear surface. These military mats are constructed of an array of rigid FRP panels connected via flexible elastomer hinges. The individual panels are typically approximately 9 mxc3x972 m (30 ftxc3x976 ft. and the hinges are approximately 7.5 cmxc3x979 m (3 inxc3x9730 ft.). A military mat is comprised of nine of these panels, thus it is approximately 9 mxc3x9716 m (30xc3x9754 ft) when unfolded. The mats are folded in an accordion (fanfold) fashion for shipment and storage. In use, the mats are unfolded, placed over the repaired pavement, and bolted to undamaged pavement. The material for the mats is a FRP resin composite. Two layers of a woven fiberglass material are embedded in a polyester resin filler to form a mat panel approximately 0.6 cm (0.22 in) thick. The perimeter of the panels is reinforced with an additional narrow strip of FRP material. The upper surface of the mat has a texture defined by the woven roving weave pattern of the FRP material. This effect is obtained by not smoothing over excess resin on the top laminate, thus yielding a non-slippery surface. The folded mat sections are heavy and require heavy equipment and substantial manpower to deploy.
Under a research work unit, several lightweight matting materials were investigated for use to build expedient roads over sands, not just for repair. AT40-MM-005, Advanced Materials for Construction of Contingency Pavement, Waterways Experiment Station (WES), U.S. Army Corps of Engineers, Vicksburg, Miss., 1997. Flat sheets of fiberglass-reinforced mat (1.2 mxc3x973.6 m (4xc3x9712 ft), similar to the U.S. Military""s Rapid Runway Repair Mat but less bulky, were tested with truck traffic over various types of sand. In order to construct a roadway for test purposes, four smaller sheets of the same mat material were placed under the edges of the larger sheets of mat and each of the larger sheets were bolted to the smaller xe2x80x9cjoinerxe2x80x9d sheets. This mat system showed promise under truck traffic but was difficult as well as labor intensive to construct. Results of this work along with recommendations for improving the mat were reported. Webster, S. and J. Tingle, Expedient Road Construction Over Sands Using Lightweight Mats, WES Technical Report GL-98-10, U.S. Army Corps of Engineers, Vicksburg, Miss., Jun. 1998.
Subsequently, the fiberglass mat design was changed to yield a square 1.8 m (6 ft) on a side after emplacement. A variety of plastic xe2x80x9cpop-in-pop-outxe2x80x9d connector pins were developed and tested for use with this design. The best plastic pin design was able to withstand 7.6 cm (3.0 in) of rutting in sand-under the mat before failing. Road demonstration tests with the fiberglass mat and plastic xe2x80x9cpop-in-pop-outxe2x80x9d pins were conducted. Santoni, R. et al., Expedient Road Construction Over Soft Soils, ERDC/GSL TR-0107, U.S. Army Corps of Engineers, Vicksburg, Miss., May 2001. The plastic pins failed in these tests.
What was needed was a simple system for effecting repairs in areas where suitable heavy equipment and materials are not readily available. Also, use of expensive hydraulic tensioners and heavy deadman apparatus was impractical to deploy to areas of varying terrain and limited accessibility. Thus, improvements in connectors for simple lightweight panels led to a preferred embodiment of the present invention. Connector pin assemblies, spacer guides, and mat hole alignment tools were designed and developed for use with the mat panels. A demonstration test road was constructed at the Waterways Experiment Station, Vicksburg, Miss., using an embodiment of this invention further described in detail below.
A preferred embodiment of the present invention uses lightweight FRP mat panels, preferably in multi-layer laminates, to fabricate a durable surface for applications such as a path, road, equipment or material pad, etc. that generally is intended for temporary use. Each mat panel comprises a flat surface area with L-shaped downward folded sides, or tabs, on two adjoining edges only. The L-shaped tabs provide a bottom ledge for connecting with the non-folded edges of adjacent mat panels. These tabs extend along each of these adjacent edges almost to the end, terminating at a distance from each end that is approximately the width of the tab. This creates a notch at each of the two corners that facilitates fitting adjoining panels.
These panels are connected in the field using specialized connectors that drop-in and are then tightened. Prior to inserting connectors along the L-shaped tabs, a specially fabricated tool is inserted in at least two of the holes in each panel into which the connectors fit in order to properly align the overlapping mats. In a preferred embodiment, the first four (4) threads of a through bolt are coated with a threadlocker such as LOCTITE(copyright) 242. Further, a specially fabricated spacer is used to properly set the desired space between the two connector plates during assembly.
A series of holes for connecting adjacent mat panels are contained on the L-shaped tab and adjacent mat panel edges. In a preferred embodiment these holes are generally rectangular with all corners radiused. A typical radius is approximately 1.0 cm (xe2x85x9c in).
In a preferred embodiment, the mat panels are sized in any dimension to facilitate manual manipulation and are light weight. For example, a panel designed to cover 3.2 m2 (1.8 mxc3x971.8 m) (36 ft2) (6 ftxc3x976 ft) when installed is fabricated from a fiberglass-reinforced plastic (FRP). It weighs approximately 52 Kg (115 pounds) and can be handled and installed easily by two workers. Because of the extended L-shaped tab, the mat itself is approximately 2.0 m (6 ft-8 in.) on a side.
For installations of a preferred embodiment, the mat panels may be connected by installing the configuration in appropriate patterns to form single-width walkways, single-lane or multi-lane roadways, or variously sized square or rectangular pad configurations. Where load-bearing capacity is not an issue, such as for personnel walkways in remote areas, it may be possible to use lighter mat panels, e.g., those comprising only two FRP laminations.
In a preferred embodiment, the connector pin assembly is comprised of a top and bottom aluminum plate that uses a hex button head or hex head cap screw with internal tooth washer to secure the connection. The aluminum plates may be machined from a high quality aluminum such as 6061-T6. The cap screw slides through the top plate and is attached to the threaded bottom plate. A spacer guide tool is used to pre-set the proper depth of the cap screw so the bottom part of the pin will clear both mat panels being connected and rotate properly during securing of the connection of the mat panels. The threadlocker is applied and provides sufficient strength for the cap screw to rotate the bottom plate 90xc2x0 in its installed location below the bottom of the lower mat panel, i.e., the area along the L-shaped tab. A cam on the top portion of the bottom plate, i.e., the portion between the two mat panels, locks in the bottom mat panel after the bottom plate rotates 90 degrees. The rotated bottom plate below the bottom mat panel then allows the connector pin to be tightened, thus locking two mat panels together along the L-shaped tab of one of them. During tightening, the threadlocker breaks under medium torque to allow the cap screw to be fully tightened.
During disassembly, the threadlocker again breaks under moderate torque allowing the cap screw to be loosened. As the pin is loosened, the threadlocker retains sufficient locking strength to force the bottom plate to rotate back 90 degrees. After rotating 90 degrees, the cain on the bottom pin plate stops the rotation of the plate to align the bottom plate with the holes in the mat panels for easy removal. The connector pin assembly may then be removed. Alternative methods for temporarily securing the pin include use of a jam nut or a vinyl pad pre-positioned in the threaded hole of the assembly. Further, to permit easy turning of the bottom plate, the bottom of the mat panels may be ribbed to provide a space between the bottom plate and the soil surface.
The connected adjacent mat panels provide a continuous flat mat surface. The mat surface may incorporate a skid resistant texture defined by a woven roving weave pattern of the top ply of fiberglass material, which is not smoothed over by use of excess resin. The cap screw is recessed into the top connector pin plate and the edges of the top plate are rounded to present a low connector pin profile on the surface of the connected mat panels.
Potential uses of the invention include expedient construction and removal of roadways, helicopter pads, aircraft parking aprons, storage pads, tent and shelter flooring, and walkways over loose sands and other unstable terrain. Duckbill type wire rope or other suitable anchors may be used to anchor the perimeter edges where mat sections are used for helicopter pads or vehicle turning and braking shifts the mat.
Advantages of the present invention include:
relatively light weight;
easy to handle by two workers;
durable connections;
easily installed;
easily removed;
damaged panels can be easily replaced during service use;
able to support heavy traffic;
cost effective;
able to be transported using standard means;
reusable;
enables minimal impact in areas of environmental fragility;
adaptable to a variety of applications;
reduced manpower to install and remove;
requires no special support equipment or installation thereof; and
standard shipping and handling procedures may be used.
The lightweight mat panels and durable connectors of a preferred embodiment of the present invention are used to construct expedient surfacing to enhance vehicle mobility over unstable terrain. Loose beach, river, desert sands or wet ground conditions frequently are not capable of supporting heavy vehicles such as tractor-trailers, aircraft, or loaded forklifts. Traffic over such unstable soils causes progressive rutting, which limits or stops the vehicle. Traditional pavement construction procedures are usually required to upgrade unstable terrain conditions in order to support heavy traffic loads on a permanent basis. These procedures require stabilizing the unstable soils with large amounts of chemical stabilizers or importing and placing substantial amounts of high-quality construction aggregates to form a base layer of sufficient strength and thickness to support the traffic loads. Traditional pavement construction procedures require substantial amounts of construction equipment, aggregate materials, and construction time. In certain applications, temporary roads must be removed and the terrain restored to its original condition once the roadway has served its intended purpose. Removal incurs additional time and expenses. Consequently, utilization of an expedient surfacing matting material that supports heavy vehicle traffic loads and may be removed quickly and stored for reuse is advantageous.